[JIT] ARM64 - Temporary fix for ldp/stp optimizations - with test fix

[TIHan]

Resolves #85765

With the latest, the code-gen is quite different from what was reported in the issue, and therefore doesn't reproduce. But the issue still exists and is able to be reproduced by a different sample:

using System;
using System.Runtime.CompilerServices;

// Expected: 515
// Actual: 0
public unsafe class Program
{
    public static void Main()
    {
        byte* bytes = stackalloc byte[1024];
        bytes[0x1A] = 1;
        bytes[0x1B] = 2;
        int sum = Foo(bytes);
        Console.WriteLine(sum);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    public static int Foo(byte* b)
    {
        return Unsafe.ReadUnaligned<int>(ref b[0x1A]) + Unsafe.ReadUnaligned<int>(ref b[0x1B]);
    }
}

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

Issue Details

---

null

Author:	TIHan
Assignees:	TIHan
Labels:	area-CodeGen-coreclr
Milestone:	-

[JulieLeeMSFT]

Please check CI is green before merging.

[TIHan]

@JulieLeeMSFT PR is green now.

[JulieLeeMSFT]

Thanks. Approved.

[TIHan]

/backport to release/8.0

[github-actions]

Started backporting to release/8.0: https://github.com/dotnet/runtime/actions/runs/5893792838